每个人的思路不一样，写出的代码也不一样，我在工作中就遇到了一个简单的例子，与你分享下，你的写法是哪种呢？欢迎回复！

题目

（不考虑缓存方案）根据ids和字典表OilDicVo获取期望的字符串:name 用/间隔的字符串。

参数

List<String> ids = Lists.newArrayList("A001", "A002", "A004", "A007");
List<OilDicVo> oilDicVos = ...;
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oilDicVos结构

[
        {
            "oilsDicId": "A001",
            "name": "89#"
        },
        {
            "oilsDicId": "A002",
            "name": "92#"
        },
        {
            "oilsDicId": "A003",
            "name": "95#"
        },
        {
            "oilsDicId": "A004",
            "name": "98#"
        },
        {
            "oilsDicId": "A005",
            "name": "87#"
        },
        {
            "oilsDicId": "A006",
            "name": "86#"
        },
        {
            "oilsDicId": "A007",
            "name": "85#"
        },
        {
            "oilsDicId": "A008",
            "name": "84#"
        }
]
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期望输出字符串

89#/92#/98#/85#
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版本V1.1

版本V1.1.0

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
StringBuilder stringBuilder = new StringBuilder();
for (String id : ids) {
 for (OilDicVo oilDicVo: oilDicVos) {
  if (ids.contains(oilDicVo.getOilsDicId())) {
   stringBuilder.append("/").append(oilDicVo.getName());
  }
 }
}
return stringBuilder.toString();
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版本V1.1.1

增加break，跳过内层循环

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
StringBuilder stringBuilder = new StringBuilder();
for (String id : ids) {
 for (OilDicVo oilDicVo: oilDicVos) {
  if (ids.contains(oilDicVo.getOilsDicId())) {
   stringBuilder.append("/").append(oilDicVo.getName());
   break;
  }
 }
}
return stringBuilder.toString();
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版本V1.2

版本V1.2.0

适用Map代替循环.

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = new HashMap<>();
for (OilDicVo oilDicVo: oilDicVos) {
 map.put(oilDicVo.getOilsDicId(), oilDicVo.getName());
}
StringBuilder stringBuilder = new StringBuilder();
for (String id : ids) {
 stringBuilder.append("/").append(map.get(id));
}
return stringBuilder.toString();
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版本V1.2.1

增加Map的初始大小

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = new HashMap<>(oilDicVos.size());
for (OilDicVo oilDicVo: oilDicVos) {
 map.put(oilDicVo.getOilsDicId(), oilDicVo.getName());
}
StringBuilder stringBuilder = new StringBuilder();
for (String id : ids) {
 stringBuilder.append("/").append(map.get(id));
}
return stringBuilder.toString();
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版本V1.2.2

减少Map的大小

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = new HashMap<>(ids.size());
for (OilDicVo oilDicVo: oilDicVos) {
 if (ids.contains(oilDicVo.getOilsDicId())) {
  map.put(oilDicVo.getOilsDicId(), oilDicVo.getName());
 }
}
StringBuilder stringBuilder = new StringBuilder();
for (String id : ids) {
 stringBuilder.append("/").append(map.get(id));
}
return stringBuilder.toString();
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版本V1.2.3

直接使用Map的Values进行循环.

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = new HashMap<>(ids.size());
for (OilDicVo oilDicVo: oilDicVos) {
 if (ids.contains(oilDicVo.getOilsDicId())) {
  map.put(oilDicVo.getOilsDicId(), oilDicVo.getName());
 }
}
StringBuilder stringBuilder = new StringBuilder();
for (String name : map.values()) {
 stringBuilder.append("/").append(name);
}
return stringBuilder.toString();
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版本V1.3

使用lambda表达式

版本V1.3.0

使用lambda表达式直接转换成Map

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = oilDicVos.stream()
 .collect(Collectors.toMap(OilDicVo::getOilsDicId, OilDicVo::getName))
StringBuilder stringBuilder = new StringBuilder();
for (String id : ids) {
 stringBuilder.append("/").append(map.get(id));
}
return stringBuilder.toString();
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版本V1.3.1

使用lambda表达式筛选可用结果后，转换成Map

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = oilDicVos.stream()
 .filter(oilDicVo -> ids.contains(oilDicVo.getOilsDicId()))
 .collect(Collectors.toMap(OilDicVo::getOilsDicId, OilDicVo::getName))
StringBuilder stringBuilder = new StringBuilder();
for (String name : map.values()) {
 stringBuilder.append("/").append(name);
}
return stringBuilder.toString();
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版本V1.3.2

使用lambda表达式筛选可用结果后，转换成Map后，直接对value值进行join处理

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
Map<String,String> map = oilDicVos.stream()
 .filter(oilDicVo -> ids.contains(oilDicVo.getOilsDicId()))
 .collect(Collectors.toMap(OilDicVo::getOilsDicId, OilDicVo::getName))
return map.values().stream().collect(Collectors.joining("/"));;
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版本V1.3.3

使用lambda一次性进行转换

List<String> ids = ...;
List<OilDicVo> oilDicVos = ...;
return oilDicVos.stream()
    .filter(oilDicVo -> ids.contains(oilDicVo.getOilsDicId()))
    .map(OilDicVo::getName)
    .collect(Collectors.joining("/"));
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总结

同一个项目里，遇见的这些类似的功能，代码大约都是其中某个版本。

• 你更喜欢哪种编码？
• 哪种编码有潜在危险？
• 哪种编码的性能最差？
• 哪种的性能最好？